Greene was indeed taking morphine. In 1998, she survived a traffic accident on an interstate highway in Tennessee. In the accident, which was not her fault, she suffered massive injuries – skull fracture, closed head injury, occipital nerve disruption, multiple rib fractures, fractured humerus and fractured pelvis. She was airlifted to hospital.

Greene was pregnant at the time of the accident but she lost the baby. In the months and years since, she has suffered from seizures, chronic pain and post-traumatic stress disorder.

She had been taking various combinations of pain medication prescribed by a neurologist and an internist who treated pain disorders. In 2003, her nursing licence was suspended for two years because of perceived impaired performance. Her chronic pain persisted and her physicians testified at trial that she needed the medications. I was there as an expert witness for the defence.
Acknowledging her need for and use of morphine was apparently damning in the eyes of the jury, but as a matter of science it is entirely irrelevant. Trace amounts of painkiller appear in the milk of women taking codeine or morphine, and a fraction (roughly 10%) ends up in the child – 2 or 3 billionths of a gram – the effects of which are negligible. No morphine-related death from breastfeeding has ever been reported in a peer-reviewed journal, and in fact the American Academy of Pediatrics recommends the use of morphine in preference to some other narcotics for women who are nursing babies.

The problems for Mrs Greene started when the police forensics laboratory found almost 50 times greater levels of morphine than would be expected in her baby – possibly enough to kill an adult. The finding warranted further investigation. Unfortunately for Mrs Greene, the additional investigative efforts were shoddy and incomplete.

If the morphine had come from the mother’s milk, one would have expected to find high concentrations of morphine in the stomach, but the dead infant’s stomach contents were not tested. If Mrs Green had been taking more morphine than prescribed, morphine metabolites would have accumulated in her blood, but her blood wasn’t tested for morphine, let alone morphine metabolites, or even her breast milk.

Her hair wasn’t tested either. Morphine is stable in hair for months, and hair analysis would have revealed whether Mrs Greene was taking more medication than had been prescribed. That test was also deemed unnecessary. In short, no real forensic investigation was conducted, just an autopsy with no diagnostic findings. If no drugs had been detected, death would have been attributed to Sids (sudden infant death syndrome or “cot death”).

Toxicologists are aware that drug concentrations in tissues increase after death. But, for the sake of argument, suppose the high levels of morphine were present at the moment the baby died. No evidence of injection was found at autopsy, leaving only two possible explanations for the excess morphine. Either a massive dose, 50-100 tablets of the type of morphine prescribed for the mother, was administered orally to the baby, or a genetic defect prevented the baby from metabolising the tiny amounts of morphine transmitted by breast milk.

The first alternative is absurd, so the only plausible explanation is a genetic defect, a possibility that is increasingly recognised within the forensic community, if not the community located in South Carolina.

In 2005, a case similar to Greene’s was reported in Toronto. A woman breastfeeding her newborn infant was taking small doses of codeine for pain related to her delivery. An enzyme in the body converts codeine to morphine, which is why small amounts of morphine would appear in the milk of any mother taking codeine. If multiple copies of the enzyme are present, too much morphine is produced and intoxication can occur. The Toronto baby died unexpectedly 12 days after birth. Autopsy blood contained a similar concentration of morphine to that found in baby Greene.

In the Toronto case, rather than initiate a homicide investigation, the medical examiner analysed the mother’s genome and found that she carried multiple copies of the codeine-converting enzyme. Instead of converting a small percentage of the codeine to morphine, she converted essentially all of it, unknowingly poisoning the infant.

A different enzyme slowly clears morphine from the infant’s blood, and children lacking this enzyme have been identified. Presumably, absence of this same enzyme was responsible for the death of baby Greene, though we will never know. The police forensics team did not perform genetic testing. The prosecutor, and all of the state’s experts, conceded that death from tainted breast milk had never been reported, but hastened to add, “There is a first time for everything.”

Around a fifth of all Sids cases are due to genetic defects. Imagine what would happen if the mother of a child born with a lethal genetic defect were to take an innocuous medicine around the time the child died as a result of his or her genetic disease. In many jurisdictions there is a good chance the mother would be charged with neglect and/or homicide since there would be no way to tell whether the drug or the genetic defect caused death. The only way to decide whether homicide had occurred would be to sequence the baby’s genome, and virtually no medical examiner in the US or the UK has the resources or inclination to do this sort of testing.

While there have been other cases of women accused of homicide by breastfeeding, the conviction of Stephanie Greene is the first case to involve a legal drug. It follows that any woman in South Carolina who takes a prescribed medication could end up being charged with a crime if the worst happened. This ruling puts every breastfeeding woman in the state at risk of the same sort of miscarriage of justice.

Dr Steven Karch is a forensic pathologist. He was assistant medical examiner in San Francisco for nearly 10 years and was an expert witness for the crown in the conviction of Dr Harold Shipman in the UK. He gave expert evidence for the defence at the trial of Stephanie Greene